U.S. Pat. No. 4,513,711 and U.S. patent application Ser. No. 783,758 filed on Oct. 3, 1985 disclose that possible rotational speed fluctuations of an internal combustion engine can be detected by means of apparatus for detecting jerk-like movements and measuring and evaluating devices. With these arrangements, the course of the rotational speed of the engine is evaluated, and fluctuations of the engine speed are established in dependence on the frequency and the intensity of rotational speed changes. This method is very complex, requiring much computing time and storage space if realized, for example, by means of a suitable programmed computer.